The success of a plant breeding program depends upon the availability of useable genetic diversity. Such diversity may be enhanced depending on the type of hybridization strategy employed. Segregating progenies resulting from F2 populations, a double cross, and a top cross were compared for the amount of useable genetic diversity associated with six traits in durum wheat. The parental lines were three winter selections, H7092-11, H7092-52, and WD5, and two spring cultivars, WPB 881 and Altar 84. Traits evaluated were (1) plant height, (2) days to maturity, (3) harvest index, (4) kernel weight, (5) grain yield, and (6) pigment content. Analysis of the population mean values suggested the superiority of the F1 top cross for plant height, kernel weight, and grain yield. The F1 top cross progeny also had the highest genetic variability for grain yield. F2 population of the cross Altar 84 I H7092-52 gave the highest mean values for days to maturity and harvest index, and showed the highest genetic diversity for traits other than grain yield. The only population showing detectable genetic variance for pigment content was the F2 progeny of the single cross WPB 881 / H7092-11. When genetic diversity was detected, the double cross was approximately intermediate between the two F2 populations from which it was derived. Transgressive segregation was more frequent in the top cross population for grain yield, kernel weight, and plant height. No associations between grain yield and the other traits were noted for the F2 population of the single cross Altar 84 I H7092-52 and the top cross population. For the second F2 population (WPB 881 / H7092-11) and the double cross population, grain yield was found to be associated with harvest index and plant height. The only consistent relationship across all segregating generations was a negative correlation between plant height and harvest index. Based on the genetic diversity and the transgressive segregation observed, top crossing appears to be the more promising in improving grain yield in the experimental material investigated. For specific traits other than grain yield, it would appear that single crosses would be a more productive approach, however progress would depend on the specific parental combination. The double cross was inferior to the other crossing strategies for the traits measured. / Graduation date: 1991

"March, 2004" / Bibliography: leaves 204-229. / xv, 229 leaves : ill. (some col.), map (col.), photos (col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The outcome of the yield evaluation trials conducted in this study was the identification of the high-yielding and widely adapted line, RH912025, which was consequently released as the variety Tamaroi. Development of B tolerant lines, with a grain yield advantage when grown under high B conditions in the field, means durum production will be able to expand into the marginal areas where B toxicity occurs. Furthermore, by pyramiding genes for B tolerance and dough strength (i.e. subunit 2*) into Tamaroi, the result should be widely grown germplasm, with premium quality for the international market. --p. x. / Thesis (Ph.D.)--University of Adelaide, School of Agriculture and Wine, Discipline of Plant and Pest Science, 2005

Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / Transient salinity in soils is characterised by high concentrations of salts in the subsoil. Durum wheat (Triticum turgidum L. Var. durum) is less tolerant of transient salinity than locally developed bread wheat (Triticum aestivum) varieties, and this results in reliable durum production being restricted to relatively unaffected soils. Field trials were conducted to assess the relative impact of transient salinity, boron toxicity and bicarbonate on crop production and highlighted the importance of combining tolerance to all three subsoil constraints into varieties intended for widespread adoption; and if the area of durum production is to be expanded. The Na exclusion locus from the landrace Na49 was found to improve the adaptation of durum to sites affected by transient salinity and is now being intogressed into a wide range of breeding material. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1152134 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture and Wine, 2005